a. Field of the Invention
The present invention pertains to a periscope-type rear view mirror apparatus for automobiles arranged so as to obtain a rear view by the use of three planar mirrors.
B. Description of the Prior Art
In known periscope-type rear view mirror apparatus, the housing for accommodating an objective mirror projects from the roof of the driver's chamber for a substantial distance, which not only is not desirable from the viewpoint of design but also causes increased wind resistance during driving. Furthermore, in such a known apparatus, the positions of the visual fields at the respective mirror surfaces of the reflecting mirror and the objective mirror undergo substantial changes as the position of the eyes moves frequently. Accordingly, it has been necessary to provide both an objective mirror and a reflecting mirror, each having the large size, in order to cover the movements of the line of vision. Thus, the apparatus as a whole tended to be large. This, in turn, is quite disadvantageous from the viewpoints such as the efficiency in attaching the apparatus to the body of the automobile, design and cost.
Also, because the reflecting mirror has a substantially large size as stated above, there arises difficulty in gaining access to the objective mirror and the window thereof when it is desired to clean these members.
Because of the foregoing circumstances, a proposal has been made to provide a periscope-type rear view mirror apparatus of compact size by the combined use of a convex lens and a concave mirror. Such an optical system, however, will cause changes in the magnification of the image or cause distortion of the image or cause disappearance of the image as the position of the driver's eyes changes. Moreover, the convex lens or the concave mirror requires a very high degree of precision in order to eliminate the distortion of the image. In addition, their combination and arrangement require a high degree of precision. As a result, a periscope-type rear view apparatus having such an optical system will have costly parts and will have poor productivity, resulting in a cost which is at least several times higher than the cost of manufacture of a periscope-type rear view mirror apparatus employing planar mirrors.
In order, therefore, to solve the foregoing various problems, the inventors developed a periscope-type rear view mirror apparatus for automobiles having an optical system comprising an objective mirror positioned on top of the roof of the driver's chamber for reflecting forwardly and downwardly the light rays coming from the rear side of the automobile into the driver's chamber, a reflecting mirror positioned substantially horizontally in the driver's chamber for reflecting upwardly and forwardly the light rays reflected by the objective mirror, and an eye-piece mirror positioned close to the reflecting mirror and having a mirror surface crossing the reflecting mirror obliquely at a sharp angle for directing the light rays reflected by the reflecting mirror to the position of the eyes of the driver, and filed a patent application under U.S. Ser. No. 426,691. In this periscope-type rear view mirror apparatus of such application, the reflecting mirror is provided within the driver's chamber and therefore the height of the protruding objective mirror can be arranged to be lower than the height of the conventional apparatus of periscope-type.
However, the periscope-type rear view mirror apparatus described in the aforesaid application has the disadvantage that it is impossible to use this apparatus as an ordinary rear view mirror of the room type when there is no need of using it as a periscope-type rear view mirror apparatus. More specifically, in order that this periscope-type rear view apparatus be more advantageous and simple to use, it should be arranged so that this apparatus can also be used as an ordinary rear view mirror apparatus whenever there is no need of using it as a periscope-type apparatus.